Wire printhead with armature biasing mechanism

Abstract

A wire printhead comprising a plurality of electromagnets and a corresponding plurality of armatures, each provided with an actuator arm forming, with the juxtaposed armature to an electromagnet, a lever of first order for actuating an impression wire attached to a free end of the actuator arm, said lever being biased to the rest position by a flexurally pre-loaded leaf spring acting on the lever in a predetermined position with respect to the lever fulcrum, through a resilient element which defines the point of application to the lever of the force from the leaf spring.

I claim: 
     
       1. A wire print head comprising a plurality of electromagnets and a corresponding plurality of armatures, each of said armatures being juxtaposed to a corresponding electromagnet and journaled thereto at an edge of said corresponding electromagnet thereby forming a related fulcrum for said corresponding armature, each of said corresponding armatures being provided with an actuation arm that extends away from said related fulcrum to form a lever of the first order for actuating an impression wire that is attached to a free end of said actuation arm; a resilient element for holding each of said levers in contact with said related fulcrum, said resilient element being offset from said fulcrum a predetermined distance in the direction of said actuation arm; and   a plurality of preloaded leaf springs applying, each through said resilient element, offset from said fulcrum, a predetermined polarization moment to a related one of said levers, said moment biasing said levers in a first rest position defined by a first abutment element for the free end of said levers.   
     
     
       2. A wire print head according to claim 1, wherein said electromagnets and said levers are radially distributed about a center axis, said armatures forming the outermost portion of said levers relative to said axis, said leaf springs being interconnected at one of their ends by a ring shaped element into a unitary leaf spring spider element lying perpendicularly to said axis. 
     
     
       3. A print head according to claim 2, wherein said resilient element is an O-ring. 
     
     
       4. A print head according to claim 2, wherein said resilient element is a ring of wear-resistant material having a prismatic cross section, a bearing surface for said leaf springs and a pressure contact wedge for said levers. 
     
     
       5. A print head according to claim 2, further including a cage of wear resistant material for supporting said leaf spring spider element including a flat ring shaped element coaxial with said axis, provided with a plurality of locating tenons arranged in a plurality of rings and housed within a shell containing said armatures, said actuator arms and said wires, said tenons positioning said leaf spring spider element, said resilient element and said armatures on said cage, said spring spider element being interposed between said flat ring shaped element of said cage and said resilient element. 
     
     
       6. A print head according to claim 5, further including means for shifting said cage in the direction of said axis between predetermined firs and second axial positions. 
     
     
       7. A print head according to claim 6, wherein said shifting means comprise a ring shaped element, housed i said shell and interposed between said cage and said shell, rotatable on said axis relative to said cage and said shell in a first and second angular position and having raised radial teeth cooperating with redial teeth of said cage for imposing said first axial position to said cage when rotated in said first angular position and said second axial position when rotated in said second angular position. 
     
     
       8. A print head according to claim 6, where said free end of said levers in abutment with said first abutment element is the free end of said actuation arms and said cage comprises a second ring shaped abutment element for the outermost free end of said armatures, said second abutment element being driven by said cage, when said cage is located in one of said predetermined axial positions, to interfere with said armatures and define a second rest position for said levers.